Use of a steering wheel locking device to deter thefts.
Also recommended are "kill switches" or starter bypass switches.
A kill switch prevents electrical current from reaching the vehicle's coil or carburetor and can only be deactivated by using a hidden switch. Before ordering the installation of a kill switch, check your vehicle's warranty policy to ensure it will not be a problem. If there is a warranty problem with kill switches, consider using a starter bypass switch to accomplish the same result. Use of a fuel switch will interrupt the flow of gas or diesel fuel and prevent the car from being driven away.
Tracking devices are useful in locating stolen vehicles.
Global positioning satellite systems that are available for a monthly or annual fee can pinpoint the location of your vehicle. Other systems allow law enforcement to directly track the car's movement.
Do not leave your vehicle running and unattended for any period of time. Many vehicles are stolen when the owner runs into a convenience store for their morning cup of coffee.